1. Technical Field The invention relates to a method for assessing the feasibility of a sub-carrier of a BPL (Broadband Power Line) signal, particularly for avoiding a mutually influencing of the BPL-signal and another signal, with the BPL-signal comprising a plurality of sub-carriers and one symbol each can be transmitted in the sub-carriers.
2. Description of Related Art
In BPL (Broadband Power Line) communication data is transmitted via the power supply network. BPL is particularly used in buildings, however it may also be utilized to provide the “last mile”, i.e. the connection of a buildings to a communication network. The data is modulated in a plurality of sub-carriers (for example 1536). The type of modulation is commonly selected separately for each sub-carrier depending on the quality of said sub-carrier. For example QPSK (Quadrature Phase Shift Keying) is used or 16 QAM (Quadrature Amplitude Modulation). The transmission usually occurs based on OFDM (Orthogonal Frequency Division Multiplexing). The BPL-frequency spectrum generally ranges from 2 MHz to 30 MHz, and thus overlaps the frequency used by various radio services. Due to the fact that a power supply network commonly is not optimized with regards to its emission behavior it cannot be excluded that the services and BPL-applications collide.
Accordingly, in practice certain frequency ranges “worth protecting” are excluded from the BPL-signal (notched), in order to avoid collisions and to ensure the coexistence of BPL and radio services. The notching of frequency ranges means in practice that individual sub-carriers of the BPL-signal are not utilized for data transmission.
In general, it can be distinguished between static and dynamic notching. In static notching one frequency range is permanently excluded, in order to protect particularly sensitive and/or safety-relevant services. Static notching can for example exclude amateur radio frequencies from the BPL-signal. In dynamic notching a frequency range is only excluded when a used signal of the radio service is actually present. Dynamic notching is presently only discussed for the frequencies of shortwave radio, because here the expansion of the service is subject to various physical phenomena, which are hard to predict. In reference to a static notching of radio transmitters, in this environment dynamic notching can increase the useful BPL-frequency spectrum by approx. 20%.
A technical challenge is presented in the detection of a shortwave signal “worth protecting”, which shows the necessary transmitter field intensity for a common receiver. One potential concept for detecting such a signal is described in DE 603 12 839 T2. Prior to starting any PLC (Power Line Communication) activity the comprehensive frequency spectrum potentially used by the PLC-system is scanned and existing radio sources are detected. Alternatively or additionally it is described that gaps in the timeframe or the frequency band are used to detect radio transmitters. Gaps in the timeframe are considered times without any PLC-activity; gaps in the frequency band are frequency ranges not used for PLC-communication. Additionally, particular correlation methods are described for a further improvement of the detection mechanisms.
In the method described in DE 603 12 839 T2 it is disadvantageous that no PLC-activity may be present when applying the method. This leads to the consequence that the entire PLC-system or at best individual sub-carriers of the PLC-system must be switched off for detection or must be deactivated. When a wanted signal changes during operation of the system this cannot be addressed in a timely fashion because first the next following inactivity phase must be waited for or intentionally initiated. This may become necessary if, for example, a shortwave radio transmitter was poorly received during the most recent detection due to atmospheric disturbances. According to the specifications of the standard ETSI TS 102578 a notch in the BPL-signal must be effective within 15 seconds after a colliding radio system has become active, i.e. the BPL-signal may be interfering the radio system for a maximum of 15 seconds. When the atmospheric interference has ceased, clear reception must be made possible within 15 seconds once more.